L312/Spring 2003 Lecture 22 Drummond April 7For today: Start Chapter 21; tissue structure and connections today (skip plant tissues)

Last time: Anaphase initiation by APC (anaphase promoting complex) : triggers inhibitor degradationactive protease degrades cohesins, metaphase progresses to anaphase

MAPs and catastrophins in maintaining a steady state involving microtubulesfailure to degrade: long strings/hairfailure to stabilize: short, unconnected

Critically compare features of microtubules and MAPs in mitosisXKCM-1 (catastrophin) and XMAP-215 (X = xenopus, a favored frog)

Finish: Steps in anaphase:anaphase A: kinetochore microtubules shortenanaphase B: interpolar microtubles lengthen and slide;

centrosomes move apart

The steps in mammalian cytokinesisThe role of actin and myosin

This time: Tissues (connective, epithelial, etc.) and the extracellular matrix What holds cells together? What gives tissues strength?

MAPs bind microtubules and modulate stability and function

XMAP215

XKCM1

Antibodydepleted

Antibodydepleted

Antibodydepleted

Implications:[MT]? [GTP]?

Actin and myosin are central to cell resolution into two cells

What are possible roles for the interpolar microtubules at thislate stage?

Initiated in anaphase

What happens to the integrins during cytokinesis?

what is the key molecular eventThat mediates integrin release?

Stepping back: cells in the context of structure

What and where is the extracellular matrix?Who makes it?What role does each cell type serve?Where do you think tumors arise?

TendonsBone CartilageEye matrix

What is the primary protein structure that provides ECM strength?

Compare to cellDimensions!

1/4th of your protein

Collagen A ~1000 aa long

(+elastin, keratin, And others)

What distinguishes these from IFs?

What are the dots?

TendonsBone CartilageEye matrix

Secretion and assembly? Fibroblasts?

How are collagenFibers crosslinked?

Vitamin C is essential for crosslinking collagen (deficiencies result in weakened skin, teeth, bones)

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James Morris couldn’t cross-link his collagen

Packing of collagen fibers leads to a banding pattern

Stripped ECM reveals collagen and fibroblasts

Perpendicular layering of collagen fibrils in skin (and elsewhere)

How do you makeCollagen fibers intoA strong skin Network?

Bone cells (osteoblasts)/osteoclasts in a connective matrix

Where is the bone?Where is the collagen?

Integrins mediate transmembrane interactionsWhat else?

The shallow lake analogy

Glycosaminoglycans (GAGs) are long, negatively charged polymers

What role do these ECM components play?Why are they sulfated?

(polymer = hyaluronan)

Proteoglycan structure in the ECM